Increase BigMath converge test precisions #954

Job	Run time
ruby-versions / Generate Ruby versions	4s
ubuntu-latest 3.4	53s
ubuntu-latest 3.2	54s
ubuntu-latest 3.3	51s
ubuntu-latest 2.7	1m 25s
ubuntu-latest 3.0	54s
macos-latest 3.4	33s
macos-latest 3.2	32s
macos-latest debug	34s
ubuntu-latest 4.0	45s
macos-latest 3.0	36s
macos-14 3.1	36s
macos-latest 4.0	40s
ubuntu-latest debug	49s
windows-latest 3.3	3m 24s
macos-14 3.2	28s
macos-14 head	27s
ubuntu-latest 3.1	52s
macos-latest head	28s
macos-latest 3.1	44s
macos-latest 3.3	41s
ubuntu-latest head	48s
windows-latest 3.4	3m 10s
macos-14 4.0	28s
macos-14 3.0	37s
macos-latest 2.7	1m 4s
macos-14 3.4	27s
windows-latest 2.7	4m 54s
macos-14 debug	29s
macos-14 3.3	29s
macos-14 2.7	1m 2s
windows-latest 4.0	2m 39s
windows-latest head	2m 55s
windows-latest mingw	2m 51s
windows-latest mswin	2m 3s
	41m 6s

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